There are many applications in which the generation of a high power, high brightness laser beam is desired. In addition, it is desirable that such a beam be efficient in terms of its energy utilization and thermal dissipation.
One approach uses an optically-pumped, high-gain, rare Earth-doped optical fiber as a gain medium with a built-in guiding structure. This is designed to have a single transverse mode, which provides intrinsically robust optical properties so that the output beam divergence of a single fiber is limited by diffraction. It has also a high thermal dissipation rate due to a large surface-to-volume ratio. However, the available power from a single device is currently limited to a few kilowatts by deleterious nonlinear effects, such as stimulated light scattering and thermally generated nonlinearities, which are aggravated by the long internal propagation length of the fiber.
An alternative approach is to combine the outputs of multiple fiber lasers in a single beam, either at the target or at the source. In such approaches, it is beneficial to maximize the number of combined lasers, but that can be limited by a number of factors.